Enhanced Alloy Recovery In Molten Steel Baths Utilizing Cored Wires Doped With Dispersants

ABSTRACT

The present invention provides increased recovery in additive-enhanced or alloy-enhanced molten steel. This is accomplished by dispersing agents blended with the additive alloys. The dispersant powder reacts with the carbon in the steel forming carbon monoxide gas which provides kinetic energy to the additive alloy particle causing dispersion within the molten bath, resulting in greater dissolution of the particles in the molten bath. The alloy or additive region is enriched, thereby improving the recovery in the molten steel.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional application No.60/938,670, filed on May 17, 2007, the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to adding alloys to moltensteel. More particularly, this invention relates to adding alloys anddispersants to molten steel in order to increase recovery in the steel.

BACKGROUND OF THE INVENTION

It is well known to add alloys and other additives to molten steel inorder to improve the material properties, including strength andtoughness, of the finished steel.

In the prior art, adding alloys and additives to molten steel is oftenaccomplished by encasing powdered alloys and additives in a metal sheathto form a “cored wire” which is subsequently “injected” into the moltensteel. U.S. Pat. No. 4,128,414 describes such an injection process. Toensure good mixing of the steel, many steel making companies employinert-gas-stirring of the molten steel. Generally, argon gas is bubbledthrough a porous plug in the bottom of the ladle or via an argon lancewhich is submerged into the molten steel from above. Often, the stirringgenerated by such devices is not sufficient to achieve good mixing and,as such, a portion of the additive alloys injected into the molten bathwill rise to the steel surface. Thus, some of the material injected intothe steel does not stay in the steel. In order to efficiently produceadditive-enhanced or alloy-enhanced molten steel, it is desirable toincrease the “recovery” in molten steel.

“Recovery” is a measure of the amount of alloy and/or additive containedin the molten steel after injection relative to the amount added.Recovery is expressed as the percent of alloy and/or additive injectedin the steel that is contained in the steel after injection. The greaterthe percentage contained in the steel after injection, the greater therecovery will be. Greater recoveries mean lower cost to the steel makerbecause less cored wire is injected.

It is well known that adding a dispersant powder to the cored wireduring its manufacture causes the additive alloy to disperse more fullywithin the molten metal, thereby enhancing the alloy and additive powderdistribution in the molten steel. This is especially true in steelmaking operations with insufficient stirring capabilities.

One known dispersant is limestone powder, which has been added to coredwire and has been shown to enhance the recovery of lead (Pb) by creatingan emulsion of the liquid lead and liquid steel. U.S. Pat. No. 4,892,580describes one such process. In U.S. Pat. No. 4,892,580, limestone wasused to facilitate reducing the size of liquid lead drops and theemulsification of the immiscible liquid lead droplets in the steel.

In another known method described in U.S. Pat. No. 4,049,433, the use ofan aqueous mixture of oil and water is added to the surface of bulkadditive alloys (e.g., larger, gravel-like chunks of additive alloysadded to a molten metal bath in bags, boxes, drums or with a shovel orchute) for the purpose of improving alloy recovery. U.S. Pat. No.4,049,433 was an attempt to disperse large pieces of additive alloysadded in bulk form to molten steel. This method, however, increases theoxygen and hydrogen content of the steel (oxygen is generally undesiredin steel and hydrogen is always undesired in steel). Further, due to thelarger size of these additive alloy particles (generally on the order of5 mm to 100 mm in diameter) and the method of adding bulk alloys tomolten baths (e.g., hand additions of cans, bags, boxes or adding looseadditions by shovel or by chute to the surface of the bath) theeffectiveness of this dispersing method is reduced.

Despite the improvements in the prior art, there remains a need toimprove upon the recovery in the molten metals, and steel in particular.

SUMMARY OF THE INVENTION

The present invention may be embodied as an alloy delivery device. Thedelivery device may include a blended substance having at least onesolid additive dissolvable alloy and at least one dispersing agent. Theblended substance may be encapsulated in a metal jacket, which may takethe form of a substantially hollow wire in which the blended substanceresides. The metal jacket is described herein as being made from steel,but other materials, including aluminum, copper or zinc, may be used.

The at least one additive dissolvable alloy may be FeNb, FeV, or FeTi.The at least one dispersing agent may be limestone. The dispersing agentmay be a powder comprised of particles having a diameter of less thanone millimeter. The additive alloy may be ground powder particles havinga diameter of less than 1 mm. The dispersing agent may be present in anamount of 5 to 50% of the mixture by weight or volume.

The present invention may be embodied as a method for providing anadditive alloy to molten metal, wherein at least one dispersing agent isblended with at least one solid additive dissolvable alloy to provide ablended substance. Preferably, the additive alloy is dissolvable. Theblended substance may be encapsulated in a metal jacket to provide analloy delivery device. Molten metal may be produced and the alloydelivery device may be injected into the molten steel. The deliverydevice may be injected into the molten steel by a wire injector andguide tube arrangement. The delivery device may be fed into the moltenmetal and the metal jacket may be allowed to melt in the molten metal,and once the jacket melts, the additive alloy, in solid particle form isallowed to mix with the molten steel, and the dispersing agentfacilitates such mixing. Depending on the alloy, the solid alloyparticles may melt, or not, after having been acted on by the dispersingagent.

It is well known that ground additive alloys (typically ground topowders under 1 mm in diameter) encased in a steel jacketed cored wirethat is injected deep into molten baths results in a significantimprovement in recovery. In this invention, the recovery is enhanced byblending limestone powder in varying amounts (typically, but not limitedto, 5% to 50% of the mixture by weight or volume) with the additivealloy that is, at least initially, introduced to the molten steel as asolid particle. The limestone has been shown to react with the carbon inthe molten metal resulting in a reaction that generates CO₂ gas. ThisCO₂ gas expands rapidly in the hot molten metal generating considerablestirring energy which imparts kinetic energy to the fine additive alloypowder upon release from the cored wire deep within the molten bath. Theextra kinetic energy causes these fine particles to be further dispersedin the bath, thus, enriching the molten metal with their chemicalelements in additive alloy depleted areas of the molten bath that, undernormal cored wire injection methods, would not be enriched. As a resultof particles being kinetically driven to further reaches of the bath,more of the bath becomes enriched, thereby increasing the recovery ofthe additive alloy.

Thus, the present invention provides an additive-enhanced oralloy-enhanced molten steel with improved recovery.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the accompanying drawings and the subsequentdescription. Briefly, the drawings are:

FIG. 1 is a flow chart of a method according to the invention.

FIG. 2 depicts an embodiment of the present invention wherein anadditive alloy is blended with a dispersant agent, which reacts with thecarbon in the molten steel, thereby providing kinetic energy to causedispersion of the additive alloy particles.

FIG. 3 depicts a cross-sectional end view of a delivery device accordingto the invention.

FIG. 4 depicts a sectioned side view of the delivery device depicted inFIG. 3.

FURTHER DESCRIPTION OF THE INVENTION

The present invention may be used to provide increased recovery inadditive-enhanced or alloy-enhanced molten steel.

FIG. 1 depicts a method according to the invention. In one such method,an additive alloy powder is blended 100 with a dispersant, such aslimestone powder, and encapsulated in a steel jacket to form a coredwire. The additive alloy may be FeNb, FeV, or FeTi. The cored wire isinjected 103 into a molten metal bath, which may be accomplished byusing a wire injector and guide tube arrangement. Then the steel jacketmelts 106 into the molten bath releasing the blended powder. Due to themelting temperature of the alloy, the alloy is released from the jacketin solid form. Since the jacket may serve to insulate the alloy, and thelimestone may serve as a heat-sink, it is possible to introduce an alloyin solid form to the molten metal even though the melting temperature ofthe alloy is at or below the temperature of the molten metal bath. Thedispersant limestone powder reacts 109 with carbon in the molten bathforming CO₂ gas which expands and moves with great energy. The energy ofthe expanding and moving CO₂ gas bubbles provides 112 kinetic energy tothe additive alloy particle and to the molten metal, thereby causinggreat dispersion of the alloy particles within the molten bath. Theincreased dispersion of additive alloy particles results in greaterdissolution 115 of the alloy in the molten bath and thus enriching moreof the bath volume with the alloy.

FIG. 2 depicts CO₂ bubbles dispersing an additive alloy particle 13. Byblending limestone powder with an additive alloy 13, and housing thatblend in an annular wire for injection into a molten bath 10, the coredwire will eventually melt, thereby exposing the limestone and alloypowders to the molten steel. By selecting alloys which are solid uponmelting of the jacket, it is believed that the alloy is dispersed betterthan the prior art. It is believed that by selecting materials toprovide the alloy as a solid, that more of the mixing energy provided bythe dispersant will be used to disperse the alloy. A chemical reactionbetween the limestone 16 and the carbon contained in the molten bath 10forms CO₂ bubbles 19, which due to the extreme temperatures of themolten bath, causes the CO₂ gas bubbles 19 to expand rapidly and withgreat energy. The energetic CO₂ gas bubbles 19 impart kinetic energy tothe additive alloy particles 13 and the molten steel 10 which, in turn,drives the alloy particles 13 further from their release point in thebath 10. By driving the additive alloy particles 13 further from theirrelease point, dispersion of the additive alloy particles 13 occurs.Thus, more of the bath volume becomes enriched in the additive alloy 13than would normally become enriched. Because more of the bath volumebecomes enriched, the recovery of the additive alloy 13 is increased.

The present invention may be embodied as an alloy delivery device. Thedelivery device may include a blended substance having at least oneadditive alloy, for example FeNb, FeV, or FeTi, and at least onedispersing agent, which may be limestone. The blended substance may beencapsulated in a steel jacket, which is a metal shell in which theblended substance resides, and which is sometimes referred to herein asa cored wire.

The above embodiment of the present invention is depicted in FIG. 3.Additive alloy 13 is blended with dispersant 16 to provide a blendedsubstance 22. The blended substance 22 is encapsulated in a steel jacket25. The encapsulated blended substance 22 and steel jacket 25 areinjected into the molten steel bath 10.

The above embodiment of the present invention is further depicted inFIG. 4. This figure depicts housing 28 for molten steel 10. In thisembodiment, a blended substance 22 contains additive alloy 13 anddispersant 16. The blended substance 22 is encapsulated in a steeljacket 25. The encapsulated blended substance 22 and steel jacket 25 areinjected into the molten steel bath 10.

In a preferred embodiment, the dispersing agent may be a powder withparticles that have a diameter of less than one millimeter, while theadditive alloy is a ground powder particle that has a diameter of lessthan 1 mm. In another preferred embodiment, the dispersing agent may bepresent in an amount of 5 to 50% of the mixture by weight or volume.

In one embodiment of the present invention, the melting temperature ofthe additive alloy is higher than the temperature of the molten steelbath. In another embodiment of the present invention, the meltingtemperature is lower than the temperature of the molten steel bath, butthe jacket is sized and/or the dispersant is selected so that theadditive alloy is insulated by the jacket and thus, the additive alloyremains as a solid inside the jacket prior to the jacket meltingthrough.

Further, it is preferable that the additive alloy is dissolvable in themolten steel. By “dissolvable,” it is meant that the additive alloy“dissolves” into the molten steel. By “dissolve” it is meant that theparticles that form the solid are released and mixed into the solution.The additive alloy remains inside the jacket as a solid and then whenthe jacket melts, the additive alloy dissolves and disperses in themolten steel. Because the additive alloy remains a solid prior to themelting of the jacket, it is not necessary for the kinetic energyprovided by CO₂ to break apart liquid additive alloy and instead theenergy that otherwise would be used to break apart liquid droplets of analloy is instead used to disperse the alloy particles. Thus, more of thekinetic energy created by the CO₂ can be directed to dispersion anddistribution of the additive alloy.

Although the present invention has been described with respect to one ormore particular embodiments, it will be understood that otherembodiments of the present invention may be made without departing fromthe spirit and scope of the present invention. Hence, the presentinvention is deemed limited only by the appended claims and thereasonable interpretation thereof.

1. An alloy delivery device, comprising: at least one solid additivedissolvable alloy; and at least one dispersing agent, the dispersingagent being blended with the alloy to provide a blended substance; and ametal jacket encapsulating the blended substance; wherein thedissolvable alloy or the metal jacket, or both are selected so that thealloy remains solid prior to melting of the jacket when the deliverydevice is added to molten steel.
 2. The alloy delivery device of claim1, wherein the metal jacket is steel.
 3. The alloy delivery device ofclaim 1, wherein the at least one additive alloy is selected from thegroup consisting of: FeNb, FeV, and FeTi.
 4. The alloy delivery deviceof claim 1, wherein the dispersing agent is limestone.
 5. The alloydelivery device of claim 1, wherein the at least one dispersing agent isa powder comprised of particles having a diameter of less than onemillimeter.
 6. The alloy delivery device of claim 1, wherein the atleast one additive alloy is comprised of ground powder particles havinga diameter of less than 1 mm.
 7. The alloy delivery device of claim 1,wherein the at least one dispersing agent is present in an amount of 5to 50% of the mixture by weight or volume.
 8. A method of providing anadditive alloy to molten steel comprising: blending at least onedispersing agent with at least one solid additive dissolvable alloy, toprovide a blended substance; encapsulating the dispersing agent andadditive alloy blend in a metal jacket to provide an alloy deliverydevice; producing molten steel; injecting the alloy delivery device intothe molten steel; allowing the jacket to melt in the molten steel;releasing the dissolvable alloy in solid form from the melted metaljacket.
 9. The method of claim 8, wherein the metal jacket is steel. 10.The method of claim 8, wherein a wire injector and guide tubearrangement is used to inject the alloy delivery device into the moltensteel.
 11. The method of claim 8, wherein the at least one dispersingagent is limestone powder.
 12. The method of claim 8, wherein the atleast one additive alloy is selected from the group consisting of: FeNb,FeV, and FeTi.
 13. The method of claim 8, wherein the method furthercomprises the step of allowing the metal jacket to melt.
 14. The methodof claim 8, wherein the method further comprises the step of dispersingthe blended substance.